Add PolicyKit checks to all the public functions, grouped
in 2 main groups: Verify and Enroll
By default, only the user is able to enroll new fingers,
or verify themselves.
You need to be allowed at least one of those 2 actions
to be allowed to claim or release the device.
We also add a new SetUsername function, for administration
functions. Users will need to be authenticate as admins to
be allowed to change the username on which the actions will
be taken. Any prints loaded before the change of username will
be unloaded.